The NL East leaders completed a three-game sweep and matched their longest winning streak of the season. The Braves play Monday at Colorado in a makeup of an April snowout, then start a series at Toronto.

Atlanta relievers set a team record, too, by extending their string to 25 scoreless innings before the Mets scored in the ninth. Mark Melancon got pinch-hitter Joe Panik to ground out with runners on first and second to end it.

Wearing all-white uniforms on Players’ Weekend, the Mets hardly looked like the team that went into this set at Citi Field with a five-game winning streak. They dropped to 5-11 against Atlanta, long their nemesis.

“They’ve beat up on us a little bit,” manager Mickey Callaway said, adding, “so we need to figure the Braves out, that’s for sure.”

A day after hitting his 30th home run, Donaldson lofted a high fly over the left field wall in the second inning and lined a drive to deep center in the seventh for his ninth long ball against the Mets this season. He tied Hank Aaron’s club mark for most homers in a year against the Mets — Hammerin’ Hank did it against the expansion club in 1962.

“I’ve had some success against them,” Donaldson said. “I have a lot of respect for their pitching staff. They know that they have good stuff, and they’re going to challenge you.”

Donaldson also had some playful, back-and-forth exchanges with the Mets crowd. No doubt, some of those same fans used to heckle another Braves third baseman, chanting “Larry, Larry” — that was Chipper’s actual first name.

“I like to interact with the fans,” Donaldson said. “Sometimes it’s more fun on the road because you know they don’t want you to have success.”

Keuchel (5-5) allowed four hits in seven innings, striking out seven and walking three. Signed by the Braves in June, the 2015 AL Cy Young Award winner exceeded his previous best start this year, when he blanked the Mets for six innings on Aug. 14.

“Fortunate to make a few pitches,” Keuchel said.

Sean Newcomb worked a perfect eighth and Melancon closed for his sixth save, including a 5-for-5 performance since being traded from San Francisco to the Braves in late July.

The Mets nicked Melancon for a run on a double by Pete Alonso, a single by J.D. Davis and an RBI forceout by Todd Frazier. Pinch-hitter Wilson Ramos singled with two outs, stretching his hitting streak to career high-tying 19 games, before Panik grounded out.

Newcomb extended the Braves’ bullpen streak to 25 shutout innings, the most since the team moved from Milwaukee to Atlanta in 1966. The prior mark was 24 2/3 innings in 2013.

Steven Matz (8-8) took the hard-luck loss. He pitched two-hit ball for six innings, striking out six with one walk.

Matz excelled despite a blister on his left middle finger that got “pretty sore.”

“It’s been pretty much coming for the whole second half. It just flares up, mainly off the slider. So, just something I have to manage,” he said.

DONALDSON DAMAGE

Donaldson connected off Paul Sewald for his 20th career multihomer game and fourth this year. He is hitting .393 (24 for 61) with a 1.381 OPS in 16 games vs. the Mets.

The record for homers against the Mets in a year is 10, by Dick Allen (1968) and Willie Stargell (1966). Atlanta closes the regular season with three games at Citi Field.

TRAINER’S ROOM

Mets: Struggling closer Edwin Díaz had “slightly improved” after leaving in the ninth inning Saturday night with tightness in his back and neck area, Callaway said. … RHP Marcus Stroman is likely to make his next start as expected, Callaway said. Stroman exited his last start with tightness in his left hamstring.